The present invention relates generally to metalhalogen batteries and more particularly to a battery of this general type which is substantially free of dendrite growth throughout its operating life.
A typical zinc-bromine or zinc-chlorine battery of the rechargeable type includes a pair of spaced apart, confronting electrode plates located within a housing, specifically a positive electrode plate constructed of porous titanium or graphite and a negative electrode plate constructed of solid titanium or graphite. One such battery system is disclosed in Applicants copending United States Patent Application Ser. No. 841,391, filed Oct. 12, 1977 now U.S. Pat. No. 4,162,351 and assigned to the Assignee of the present application. In the zinc-chlorine battery, a single stream of electrolyte solution may be passed through the housing and a separator is not required.
One major problem in the development of a rechargeable metal-halogen battery of the general type just described has resided in the inability to reliably eliminate or control dendrite growth. More specifically, in this type of battery, it is necessary to provide the proper spacing between the electrode plates which, in turn, requires the utilization of some form of rigid spacing ribs between the plates, particularly for electrode dimensions of practical interest (i.e. plates having large surface areas and thin cross-sections) where uncontrollable bowing may otherwise result. However, studies have shown that there is a tendency for dendrite growth to propagate along the region of contact between the separator ribs and the negative electrode which is in contact with the ribs. Applicants have found this to be a result of electrolyte flow stagnation in this region of contact, which nonetheless receives approximately the same current density as the rest of the electrode. In other words, Applicants have found that reduced solution flow at the rib contacting region of the negative electrode at the operating current density of the battery has resulted in dendritic metal deposition. As will be seen hereinafter, the present invention minimizes and preferably eliminates dendrite growth by providing region located adjacent each rib which region displays insufficient current density and/or too high of an electrolyte flow rate to support dendrite growth.